Two-layer wide-band meander-line polarizer

ABSTRACT

A two-layer polarizer ( 6, 7 ) comprising a first substrate ( 10 ) having formed on a major surface thereof a first conductive meander line array ( 2 ) and a second substrate ( 12 ) having formed on a major surface thereof a second conductive meander line array ( 3 ). The first and second substrates are disposed as adjacent layers and are separated by a dielectric space ( 8 ). At least a portion of the first meander line array and a portion of said second meander line array are overlapping.

This application claims the benefit of U.S. Provisional Application No.60/283,917, filed Apr. 13, 2001, under 35 U.S.C. § 119(e).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention disclosure relates to a meander-line polarizer,particularly a polarizer having only two printed layers and operative toprovide wide-band performance with a low axial ratio. The polarizer isespecially useable in aperture-type antennas, particularly antennasoperative to convert electromagnetic field polarization from linear tocircular and from circular to linear.

2. Background of the Invention

In the related art, two orthogonal senses of linear polarization in amultilayer printed circuit structure can be produced, as well as asingle circular polarization using a multilayer printed circuitstructure having a meander line conductor. Previous designs of meanderline polarizers used 3 to 4 layers of printed circuits to achieve therequired axial ratio for the circular polarization across the band. Theprinted layers are separated by supporting dielectric substrate layersthat are quarter-wavelength-thick. Such meander-line polarizers areexpensive to manufacture and are undesirably thick. However, the relatedart does not disclose or suggest use of a two-layer meander linepolarizer, particularly one with low axial ratio over a wide bandwidth.More specifically, the use of only two meander line layers to convert alinear polarization into a circular polarization for a single or dualsenses of circular polarization has not been demonstrated as achievablein the related art. Thus, the aforementioned related art structure hasat least the disadvantage of requiring extra layers in the printedcircuit polarizer, which results in an increased cost, if production ofan output having a single sense or two orthogonal senses is desired.Even more specifically, the prior art does not disclose an antenna incombination with a two layer meander line polarizer.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome at least theaforementioned problems and disadvantages of the related art system.

It is another object of the present invention to minimize a number oflayers present in a multilayer structure of a polarizer, thus minimizingcost and size of the polarizer.

Accordingly, a first feature of the invention involves a two-layerpolarizer comprising a first substrate having formed on a major surfacethereof a first conductive meander line array and a second substratehaving formed on a major surface thereof a second conductive meanderline array. The first and second substrates are stacked with their majorsurfaces in parallel as adjacent layers that are separated by adielectric space. The separation of the two layers is less than quarterwavelength.

A second feature of the invention involves a combination of an antennahaving at least one aperture, and a two layer polarizer disposed overthe at least one aperture. The two-layer polarizer includes a firstsubstrate having formed on a major surface thereof a first conductivemeander line array; and a second substrate having formed on a majorsurface thereof a second conductive meander line array. The first andsecond substrates are disposed with their major surfaces in parallel asadjacent layers that are separated by a dielectric space. The separationof the two layers is less than quarter wavelength.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of illustrative, nonlimiting embodiments of the presentinvention and are incorporated in and constitute a part of thisspecification, illustrate embodiments of the invention and together withthe description serve to explain the principles of the presentinvention.

FIG. 1 illustrates a configuration of the meander line polarizer layersaccording to the exemplary embodiment of the present invention.

FIG. 2 illustrates a detailed configuration of the dimensionalrelationship of the two meander line polarizer implemented in accordancewith the present invention.

FIG. 3 illustrates a graphical representation of a measured axial ratioof the meander line polarizer over 500 MHz bandwidth according to thepresent invention.

FIG. 4 illustrates a graphical representation of a measured axial ratioof the meander line polarizer over 2 GHz bandwidth according to thepresent invention.

FIG. 5 illustrates an antenna in combination with a two-layer meanderline polarizer disposed across the antenna aperture, according to anexemplary embodiment of the invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS OF THE INVENTION

Reference will now be made in detail to an illustrative, non-limitingembodiment of the present invention, examples of which are illustratedin the accompanying drawings. In the present invention, the terms aremeant to have the definition provided in the specification, and areotherwise not limited by the specification.

The present invention includes a first meander line polarization layerhaving a first conductive meander line array disposed on a major surfaceof a first substrate and a second meander line polarization layer havinga second conductive meander line array disposed on a major surface of asecond substrate. The two substrates are separated by a distance that isless than one quarter wavelength. In the illustrated example, thedistance is 0.15 of a wavelength. The meander line polarizer layersintroduce phase shifts and signal decomposition, which leads todecomposing the signals into two sets of orthogonal linear polarizationsat phase quadratures to produce circular polarizations. The arrangementof the above-disclosed layers is described subsequently in greaterdetail with respect to the drawings.

As a result, low axial ratios (e.g., approximately 1 dB to 2 dB) can beobtained over antenna beam width and over a wide frequency band (e.g.,greater than about 20%). Also, the minimization of the number of printedcircuit layers for a transmission device, by having only two meanderline polarizer layers, results in the reduction of production cost ofthe transmission device, e.g., an antenna. The printed circuit two-layermeander line polarizer converts signals with a single or dual linearpolarizations into a single or dual circular polarizations. The designof the array and the two-layer polarizer can be scaled to differentfrequency bands.

FIG. 1 shows a front view of the meander line polarizer 1 having twooverlapping meander-line layers 6, 7 according to the preferredembodiment of the present invention. Each layer 6, 7 includes arespective meander line conductive strip array 9, 11. Each array has aplurality of parallel conductive strips 2, 3, respectively, and eachstrip is formed with a periodic and substantially square wave patternthat follows a longitudinal axis 4, 5. The meander line strip arrays 9,11 are distributed homogeneously on a major surface of respective thindielectric substrates 10, 12, which are made of Mylar in an exemplaryembodiment. The two meander line layers 6, 7 are separated by adielectric 8, as shown in FIG. 1. FIG. 1 further illustrates that themeander line conductive lines 2, 3 on a respective one of the meanderline strip arrays 9, 11 on each of the respective meander line layers 6,7 are printed at a 45° angle with respect to the polarization directionof a linearly polarized wave.

In operation, the two-layer meander-line polarizer 1 is used to transferthe linear polarization of propagation waves into a circularpolarization. The structure of each meander-line strip array 9, 11 isdesigned to be predominantly inductive to one linear polarization andpredominantly capacitive to the orthogonal linear polarization. Accuratespacing between two meander-line layers or sheets 6, 7 can be achievedby using low loss polyfoam as the dielectric 8 at a desired thickness.The structure of the polarizer can convert linear to circularpolarization according to the following principle. The incident linearlypolarized wave can be resolved into two equal linearly polarizedcomponents at ±45° relative to the incident wave. The meander lines 2, 3on each of the respective polarizer layers are oriented at 45° relativeto the incident wave. The two orthogonal components are in-phase whenincident on the polarizer. On passing through the polarizer, onecomponent goes through an inductive phase change, while the orthogonalcomponent goes through a capacitive phase change. If a phase shift of90° is achieved by the two wave components when they pass through thepolarizer, a circularly polarized wave is generated.

The parameters that define the geometry of the periodic squarewave-shaped meander-line array 9, 11 for each of the meander line layers6, 7 are illustrated in FIG. 2. The width of the conductive material inthe meander-line array W1 is a width of the conductor in thelongitudinal direction (i.e., in the direction 4, 5) of the metalizedline on the plane of the layers 6, 7, while the width W2 is thedimension of the conductor in a direction orthogonal to the longitudinaldirection. The height of the meander-line B, which is the spacingbetween the apicies of the periodic square wave, is measured in theplane of the meander line layer 6, 7, while the period of the meanderline is identified as A. The width parameters W1, W2 and the height Bdetermine the operating frequency and the bandwidth of the polarizer.The distance H between each meander-line 2, 3 in each respective array6, 7 determines the phase shift of each layer. For circuit matchingpurposes, layer 6 and layer 7 have different parameter values. While asquare wave pattern is preferred, modifications to such periodic patternmay be utilized, as would be known to one skilled in the art. TABLE IDimensions of each layers of the polarizer (inches) Layer # A B H W1 W2Spacing 6 0.166 0.110 0.254 0.013 0.018 0.094 7 0.240 0.180 0.254 0.0300.040

Table I lists the parameter values of an exemplary embodiment of thetwo-layer meander-line polarizer 1 which operates at the frequency bandfrom 10.75 to 12.75 GHz. The spacing between the meander-line layers isabout 0.094 inches, which typically is the thickness of the dielectricsupport layer 8, and does not include the thickness of the Mylarsubstrate that comprises the layers 10, 12. This spacing issubstantially less than a quarter wavelength and is critical toachieving the right phase relationship that produces the circularpolarizations. The measurement results of the axial ratio over the 500MHz bandwidth defined over a range of 12.2 Ghz to 12.7 Ghz are shown inFIG. 3 and substantially demonstrate maximum value of around 1 dB. Themeasured value of the axial ratio for 2 GHz bandwidth between 10.75 GHzand 12.75 GHz is about 2 dB as shown in FIG. 4.

FIG. 5 illustrates a schematic of a combination 50 of an antenna 51 anda two layer polarizer 52, in accordance with the present invention. Theantenna may be of any type, including a flat plate antenna or a hornantenna with a feed. The polarizer would be disposed at the aperture ofthe antenna and would provide the conversion between linear and circularpolarization, as disclosed herein.

A significant result of the present two-layer meander-line polarizer isthat the polarizer can be used with a wide variety of aperture-typeantennas converting electromagnetic field polarization from linear tocircular polarization, or conversely from circular to linearpolarization. Also, low axial ratio (1 or 2 dB) can be obtained overantenna beamwidth and over a wide frequency band (over 20%). Indeed, theachievement of a high frequency band is a dramatic improvement over thebandwidth that previously had been limited to 16% or 17%.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the described illustrativeembodiments of the present invention without departing from the spiritor scope of the invention. Thus, it is intended that the presentinvention cover all modifications and variations of this inventionconsistent with the scope of the appended claims and their equivalents.

1. A two-layer polarizer comprising: a first substrate having formed ona major surface thereof a first conductive meander line array; a secondsubstrate having formed on a major surface thereof a second conductivemeander line array, said first and second substrates being disposed asadjacent layers and separated by a dielectric space, at least a portionof said first meander line array and a portion of said second meanderline array overlapping.
 2. A two-layer polarizer as claimed in claim 1,wherein said dielectric space is less than ¼ λ, where λ is thewavelength of an incoming wave.
 3. A two-layer polarizer as claimed inclaim 2, wherein the dielectric space is approximately 0.15 λ.
 4. Atwo-layer polarizer as claimed in claim 1, wherein said dielectric spacecomprises an insulating material.
 5. A two-layer polarizer as claimed inclaim 1, wherein said first meander line array and said second meanderline array comprises a plurality of conductive strips, each having asquare wave shape.
 6. A two-layer polarizer as claimed in claim 5,wherein said square wave shape comprises a period A, a height B, ahorizontal width W1 and a vertical width W2.
 7. A two-layer polarizer asclaimed in claim 6, wherein the operating frequency and the bandwidth ofthe polarizer are determined by the values of B, W1 and W2.
 8. Atwo-layer polarizer as claimed in claim 1, wherein said meander line isextended at approximately 45° with respect to a polarization directionof a linearly polarized wave.
 9. A two-layer polarizer as claimed inclaim 9, wherein said wherein said substrate comprises Mylar.
 10. Atwo-layer polarizer as claimed in claim 9 wherein said dielectric spaceis filled with low loss polyfoam.
 11. A two-layer polarizer as claimedin claim 1, wherein said polarizer exhibits an axial ratio of 2 db at 2Ghz.
 12. A two-layer polarizer as claimed in claim 1, wherein saidpolarizer exhibits an axial ratio of approximately 1 dB at a bandwidthof approximately 500 Mhz.
 13. A two-layer polarizer as claimed in claim7, wherein said parameters are scaled to different frequencies
 14. Atwo-layer polarizer as claimed in claim 1, wherein said axial ratio of 2dB is for a signal at approximately 11-13 Ghz.
 15. In combination, anantenna having at least one aperture, and a two-layer polarizer disposedover said at least one aperture and comprising: a first substrate havingformed on a major surface thereof a first conductive meander line array;a second substrate having formed on a major surface thereof a secondconductive meander line array, said first and second substrates beingdisposed as adjacent layers and separated by a dielectric space, atleast a portion of said first meander line array and a portion of saidsecond meander line array overlapping.
 16. A combination as claimed inclaim 15 in which said two-layer polarizer dielectric space is less than¼ λ, where λ is the wavelength of an incoming wave.
 17. A combination asclaimed in claim 16, wherein the dielectric space is approximately 0.15λ.
 18. In combination, an antenna having at least one aperture, and atwo-layer polarizer means disposed over said at least one aperture fortransferring a linear polarization of propagation waves into a circularpolarization.
 19. The combination as set forth in claim 18, wherein saidtwo layer polarizer means is operative to introduce phase shifts andsignal decomposition, which leads to two orthogonal linear polarizationsat phase quadrature to produce circular polarization.
 20. Thecombination as set forth in claim 18, wherein said combination providesan axial ratio less than or equal to 2 dB.